[Feature] Add OpenTelemetry observability integration

[imran-siddique]

Problem

The toolkit ships with no native OpenTelemetry traces, Prometheus metrics, or pre-built dashboards. Security and ops teams need to see policy violations, trust scores, and termination events in their existing observability stack.

Proposed Solution

• Export OTEL spans for every policy decision
• Prometheus metrics endpoint (violation rates, trust score distributions, termination events)
• Pre-built Grafana/Azure Monitor dashboard templates
• Match Microsoft Agent Framework OTEL observability baseline

Related

Microsoft Agent Framework already ships with OpenTelemetry support. The Governance Toolkit should match that baseline.